1. Field of the Invention
The present invention relates to integrated network systems of different types of network systems, and, in particular, to a packet signal frame format for supporting frame formats used in the different-type network systems integrated.
2. Description of the Prior Art
As digital data communication systems, there are some different-type network systems wherein the packet signals are formed according to different frame formats from one another. For example, an LAN (Local Area Network) system accommodates a plurality of terminal equipments or devices which are assigned with different addresses. When a terminal equipment intends as a source to transmit a data unit to another equipment as a destination through the LAN network, it is required for its source terminal equipment to form a packet signal including the own address as a source address, an address assigned to the other terminal equipment as a destination address, and the data unit according to a packet signal frame format prescribed in the LAN system.
In an integrated services digital network (ISDN) system recommended in the CCITT (International Telegraph and Telephone Consultative Communication) recommendations I series, those destination and source addresses are not used for media access control between terminal equipments through the network.
For integration of a plurality of different-type network systems, a multiple frame format approach and a single frame format approach are proposed in a paper entitled "ON the IEEE 802.9 Data Link Formats for the Case of Logically Out-of-band D-channel", IEEE 802.9 contribution, 1988 (Reference 1).
According to the multiple frame format approach, a frame or format identifier is added to frames used in individual network systems so as to distinguish the individual frames. This approach is advantageous for a certain integrating form of different-type network system. However, it is not utilized for some other integrating forms of the different-type network systems, because the approach is independent of respective network systems.
According to the single frame format approach, a specific frame format among different network systems is commonly used for transmission of other frames. This approach is advantageous for the specific network system but disadvantageous for the other network systems. For example, in integration of the LAN system and the ISDN system, the LAN frame is used by addition of the destination address and the source address to the ISDN frame. In this approach, it is necessary for terminal equipments to access the ISDN network through the LAN network.
Accordingly, both of the approaches proposed in Reference 1 have a limit for application on various forms for integrating different-type network systems.